Delay time computer for heart pump system



March 4, 1969 w J. FL ANAGAN ET AL. 3,430,624

DELAY- TIME COMPUTER FOR HEART PUMP SYSTEM Sheet Filed Sept. 7,` 1966Wmv March 4, 1969 l W J, FLANAGAN ET Al. 3,430,624

DELAY TIME COMPUTER FOR HEART PUMP SYSTEM March 4, 1969 w. 1. FLANAGANET AL 3,430,624

DELAY TIME COMPUTER FOR HEART PUMP SYSTEM Sheet Filed sept. v, 1966 KSUWQ QQSQ www United States Patent O aware Filed Sept. 7, 1966, Ser. No.577,680 U.S. Cl. 12S-1 Int. Cl. A61m 5/14; A61h 31/00 9 Claims ABSTRACTOF THE DISCLOSURE A heart pump system includes a triggered functiongenerator for lgenerating a variable delay which defines the time that aheart pump stroke should be delayed from the R wave of a patients EKGwaveform. The delayed time is computed from the function 10.21 VR-R-i-K,where R-R is the cardiac period, and K is a manually set constant. Thesystem includes a two-channel cycle time computer for counting timebetween R waves, in each of two channels, alternatively. The cycle timecomputer controls a pump cycle computer along with the output of thedelayed time computer. A withdraw stroke sensor prevents the delay timecomputer from operating the pump cycle computer sporadically, by meansof a gate. The pump cycle computer is controlled by a regenerativeswitch to operate the pumped stroke driver of a blood pump during oneportion of the cycle, and operate the withdraw stroke driver of theblood pump in another part of the cycle.

This invention relates generally to a device for assisting or replacingthe natural action of a defective heart. More particularly it concernsan apparatus for assisting or replacing insufficient natural heartaction by automatically synthesizing the parameters of the patientsphysiological heart waveform.

It relates to an improvement over the heart pump system shown in thecopending application of Merrill G. Chesnut et al., Ser. No. 406,722,filed Oct. 27, 1964, and assigned to the assignee of the presentinvention. This prior system has the basic objective of reducing thework load of the heart by lowering the pressure head against which theventricle must eject its contained blood and to aid the coronarycirculation by increasing the blood pressure and flow during the correctphase of the natural heart cycle regardless of changes in the naturalheart rate. This phase corresponds to the period of time when theresistance to coronary circulation is at a minimum and has been found tobe in what is described as the post-systolic period.

This prior system includes a reciprocating blood pump connected inclosed circuit fashion to a single or double catheter adapted to beinserted into the patients femoral arteries. The cycle of thereciprocating pump may be divided hemodynamically into a withdrawal timeand a push time corresponding to the reciprocating strokes of the pump,and it is further electrically governed by a third parameter, i.e., thedelay time which is the. phase lag of the pump cycle with respect to thecardiac cycle. Other variables in the cycle are the volume of blood tobe pumped per cycle of the patients natural heart period, the rate ofwithdrawal of the blood through the catheter, and the rate of injectingblood into the aorta during the push phase. For a given catheter, themaximum negative pressure which can be obtained is theoretically aperfect vacuum minus some small amount for vapor pressure, andtherefore, there is a certain maximum rate at which blood can be removedfrom the vascular tree through a catheter of given length and bore. Acertain volume of blood must be removed from the aorta to produce thedesired pressure drop Within the aorta, and for this reason there is aminimum withdrawal time to remove that volume. If this is exceeded,cavitation and degassing of the blood will occur with increasedhemolysis. Also, there is a limit on the maximum rate at which blood maybe pushed into the aorta and this limit is determined by the point atwhich cerebral vessel damage could be caused by excessive pressure. Forthese reasons, the maximum allowable Withdrawal and push rates are neverexceeded in the above mentioned prior system regardless of changes inthe patients natural heart period or rate.

However, for a given heart beat rate or heart cycle period, it is notalways desirable to deliver the maximum volume of blood to the patientsaorta. In this event, the device described in the above application inresponse to the selection of a lower than maximum volume automaticallyadjusts pump and withdrawal rates below their maximum values inaccordance with a predetermined complex function to achieve the newdesired volume. This complex function reduces the ratio of the pump tothe withdrawal time as it is advisable to increase the withdrawal timeas much as possible as the withdrawal rate effects on the blood are morecritical than the push rate.

In addition to automatically varying the above pump cycle parameters,this prior device automatically compensates for changing heart rates bycomputing new withdrawal and pumping rates and sometimes eifects anautomatic change in the volume of blood pumped when the maximum bloodpumping rates have been reached. 'This occurs at a time when thepatients heart rate is extremely fast. With normal variations in heartrate the device has no effect on the volume of blood pumped. However,when 4the heart rate varies widely to the point where the maximumpumping rates would have to be exceeded to pump the desired quantity ofblood, the control system computes a new lower volume compatible withthe maximum withdrawal and pump rates so that the pumping cycle equalsthe patients heart cycle time.

The above described system, and other heart pump systems known in theprior art have what may be termed as a iixed delay time. 'I'he delaytime may be defined as that interval of time between a selected portionof the R wave of the patients EKG waveform (which is used as the inputparameter to the system) and the actual initiation of the pumping cycle.This delay time is extremely important to achieve proper phasing of thepump With the patients natural heart action. It has been determinedphysiologically that a phase relationship exists which reduces theintraventricular pressure to a minimum for a given volume pumped andincreases the post-systolic arterial pressure to an extent which returnsthe intraaortic pressure to its prepump level or better so that coronaryand peripheral circulation may be assisted. This phasing has beenfoundito be most effective when the push phase of the pumping cyclebegins after or at the peak of the intraventricular waveform with thepush phase continuing during the systolic period, and the withdrawalphase begins immediately upon completion of the pumping phase andcontinues during aortic valve opening thereby aspirating the leftventricle into the aorta with the withdrawal phase continuing until thepeak of the next intraventricular waveform at which time another pumpingor push phase begins in response to another triggering signal.

It is apparent from the above that the proper phasing of the pumpingcycle with the cardiac cycle is dependent to a large extent upon thetime between the selected portion of the R wave of the patients EKGwaveform and the peak of the intraventricular waveform. However,

3 the duration of the intraventricular waveform has been found to varyas a function of heart rate, and therefore, the delay required forproper phasing should also vary. Prior known systems are not -capable ofany automatic variation in this delay time.

As a result of physiological experimentation now of general knowledge,it has been determined that the variation in duration of theintraventricular waveform with the heart rate can be predicted with someconfidence. This experimentation has indicated that the Q-II-A intervalbetween the onset of the electrocardiograms QRS complex and the onset ofthe second heart sound of aortic origin may be approximated by theequation Q-II-A=10.21\/R-R|K, where R-R is the cardiac cycle period inmilliseconds, and K is a constant number of milliseconds for a specificindividual.

Since the pump trigger pulse is initiated by the R portion of thepatients EKG Wave, which bears a relatively fixed relationship to theonset of the Q-R-S complex, and since the desired arrival time of thepump pulse at or after the peak of the intraventricular waveform is inthe close vicinity of aortic incisura, which is intimately associatedwith the second heart sound of aortic origin, proper phasing of the pumppulse with heart rate variations may be achieved by variation of thepump trigger delay directly with the function 10.21\/R-R.

It is therefore a primary object of the present invention to provide anew and improved heart pump system of the type having each pumping cyclephased with respect to a sensed physiological parameter of the patientwith means for automatically varying the delay of the pumping cycle withrespect to the sensed parameter.

Another object of the present invention is to provide a new and improvedheart pump system of the type described above which computes in responseto changes in the patients heart rate the proper delay of each pumpingcycle with respect to the QRS complex of the patients EKG waveform.

A further object of the present invention is to provide a delay timecomputer circuit for a heart pump of the. type described above having adual channel circuit which computes a signal representing the desireddelay time in one channel while reading out of the other channel duringone heart cycle and thereafter reverses so that on the next heart cyclethe first channel will be read out and the second channel will compute anew delay time so that the circuit has a memory function.

A still further object of the present invention is to provide a heartpumping system of the type described above with a delay time computercircuit which converts `a voltage representing the computed functioninto a time base with a resettable linear ramp generator and aunijunction transistor circuit.

Other objects and advantages will become readily apparent from thefollowing detailed description taken in connection with the accompanyingdrawings, in which:

FIGURE 1 is a block diagram of a heart pump system according to thepresent invention;

FIGURE 2 is a block diagram of the automatic delay time computer circuitshown in FIGURE 1;

FIGURE 3 is a schematic drawing of the delay time computer circuit; and

FIGURE 4 is a graph showing the computed relationship between delay timeand the cardiac cycle period.

While an illustrative embodiment of the invention is shown in thedrawings and will be described in detail herein, the invention issusceptible of embodiment in many ditferent forms and it should beunderstood that the present disclosure is to be considered as anexemplication of the principles of the invention and is not intended tolimit the invention to the embodiment illustrated. The scope of theinvention will be pointed out in the appended claims.

Referring now to FIGURE 1, a block diagram of a heart pumping system isshown generally similar to that disclosed in the above mentionedcopending application of Chesnut et al. For this reason only the generalfunction and operation of the overall system will be described in orderto clearly illustrate the environment for the present delay timecomputer circuitry, but it should be understood that reference should bemade to the copending application of Chesnut et al. for the details ofcomponents.

As shown, the circuit is generally adapted to receive as an input signalthe patients EKG waveform, delay the signal, and after various computerfunctions drive the pump and withdraw servo coils 10 and 11 in anassociated pump servo motor. A triggering circuit is provided effectiveto develop and delay a triggering pulse for a reciprocating pump anddelay the triggering pulse from a selected trigger level portion of theQRS segment of the patients EKG waveform. For this purpose, a triggerlevel selector 13 is connected to receive the patients EKG waveform froma. conventional electrocardiogram through line 16. Suitable provisionmay be made for driving an oscilloscope from the EKG signal so that thepatients waveform may be viewed during the use of the heart pumpingsystem by the surgeon or technician. The trigger level selector 13includes a manually adjustable trigger level potentiometer 14 to selectthe proper or desired triggering level on the QRS waveform.

As noted in the above mentioned copending application, pump cycletriggering may be alternatively provided by a pacemaker, or by a manualinitiation switch.

The undelayed triggering pulse (synchronous with the selected portion ofthe patients R wave) from the trigger level selector 13 is delayed by adelay time computer circuit 15 so that the actual triggering pulse lagsthe selected portion of the patients EKG waveform. In addition toreceiving the triggering signal as an input, the delay time computerreceives a signal, designated En, from a heart cycle time computer 18.

The heart cycle time computer 18 may be similar to the digital cardiaccycle counting circuit shown in the above copending application, whichcircuit responds to an arterial pump pressure signal, or the patientsEKG signal, to digitally count in either of two channels the time periodbetween arterial pulses or R waves depending on whether pressure or EKGis used as the input parameter. The digital counting circuit provides alinear output voltage with time proportional to the cardiac interval.This is represented by E1n in FIG. 1. The counted heart cycle time fromthe computer 18 is also applied to a pump cycle computer 20 as inputparameter for determining the duration, speed, and magnitude of eachpumping cycle.

The output from the delay time computer 15, which is properly phasedwith respect to the trigger signals from the trigger level selector 13,triggers a refractory gate 22 which produces an 8O millisecond pulsewhen triggered.

The pulse from the refractory gate 22 comprises one of two inputs to ANDgate 25. AND gate 25 prevents any erroneous triggering signal from therefractory gate 22 from initiating a pumping cycle. That is, if thetriggering pulse from the refractory gate 22 is conducted to the ANDgate 25 prior to the receipt of a signal from the other input to ANDgate 25, i.e., line 28, which indicates completion of the withdrawalstroke, the millisecond pulse will be held by the AND gate for 80milliseconds and if line 28 is not energized by that time, thetriggering pulse will be dropped. Line 28 is energized by suitabletransducer 30 connected to pump servo mechanism 32 indicating that thewithdrawal stroke of the pump has been completed.

A pulse in line 32 from AND gate 25 initiates the push phase of thepumping cycle by turning on a regenerative switch 34. The presence ofthe high voltage in line 32 turns the first stage of the regenerativeswitch on and the second stage off thereby energizing line 36 anddeenerizing line 37. Line 36 energizes a pump servo coil 40 through thepump cycle computer 20 (volume and rate computer crcuitry),- while theencrgization of line 37 energizes the time represented by the timebetween initiation of a ramp voltage and the firing -of the unijunctiontransistor 96.

In an exemplary operation of the present device, and viewing the graphof FIG. 4, assume that a patients heart rate is 75 beats per minute (acardiac cycle period of 800 milliseconds), and that the initial settingof the manual vernier 64 corresponds to a K of minus 100 milliseconds.The function generator 66 will then compute a time delay of 188.8milliseconds for the variable delay circuit 65. Further assume that forthis particular patient and heart rate the proper pump trigger delay is130 milliseconds. When the pump is activated, the operator will observethat the intraventricular waveform display on an oscilloscope indicateslate pump phasing by 58.8 milliseconds. He, therefore, would then adjustthe manual vernier 64 for proper pump phasing and thereby automaticallyadjusting K to the proper value of minus 158.8 milliseconds for a 130millisecond delay at 75 beats per minute. If the patients heart rateshould then change to, for example, 125 beats per minute (a cardiacperiod of 480 milliseconds) the position of the heart pressure wavesdichrotic notch will advance in time by 65.1 milliseconds. The functiongenerator 63, however, will automatically compute the proper delay timeas follows:

milliseconds which of course is 65.1 milliseconds less than the originaldelay of 130 milliseconds.

We claim:

1. In a heart pump system, the combination comprising: pump means havingpumping cycles, means connected to the pump adapted to convey fluidrelative to the patients circulatory system, control means for said pumpmeans including means for initiating the pumping cycles in timedrelationship with a physiological parameter, said means for initiatingpumping cycles including means for delaying the intiation of a pumpingcycle relative to a portion of the physiological parameter, and meansfor automatically varying the time of said delay with variations in saidphysiological parameter.

2. In a heart pum-p system, the combination comprising: a pump havingpumping cycles, means connecting the pump for conveying fluid relativeto the patients circulatory system, control means for said pumpincluding means for initiating each pumping cycle in timed relationshipwith one of the patients cyclical circulatory parameters, meansresponsive to the period of said cyclical parameter for computing theduration of each pumping cycle, control means responsive to saidcomputing means for varying each pumping cycle, means for delaying eachpumping cycle Iwith respect to a selected portion of said cyclicalparameter, means for computing the proper time of said delay withvariations in the period of said cyclical parameter, and control meansresponsive to said means for computing delay for varying said delaytime, whereby each pumping cycle will be initiated at a predeterminedpoint relative to the patients intraventricular waveform regardless ofthe repetition rate of said cyclical parameter.

3. The combination defined in claim 2, wherein said means for initiatingeach pumping cycle includes means for receiving a signal representingthe patients EKG waveform, means for selecting a portion of the R wavethereof and deriving triggering signals therefrom, said means fordelaying being responsive to said triggering signals, means forcomputing the time duration of one of the patients cyclical circulatoryparameters Iand deriving a signal representing the same to determine thecardiac period, said delay computer being responsive to said signalrepresenting the time duration of said circulatory parameter forderiving a signal as a nonlinear function thereof representing thedesired variation in delay time with cardiac period, said means fordelaying being responsive to said delay computer for producing pumptriggering signals delayed from said R wave.

4. The combination defined in claim 3, wherein said delay computerincludes a function generator for generating the nonlinear function as afunction of the duration of the intraventricular waveform with cardiaccycle time.

5. The combination as defined in claim 4, wherein said functiongenerator includes means to generate a signal proportional to thefunction X\/R-R{K, where X and K are constants and R-Ris the cardiacperiod.

6. The combination as defined in claim 5 wherein parameters of saidfunction generator are chosen so as to derive a signal proportional to afunction in which said constant X is approximately 10.21 so that eachpumping cycle is initiated approximately at aortic valve closure.

7. The combination defined in claim 4 wherein said delay computerincludes a function generator responsive to said signal representing thecardiac period, two selectively operable track and hold channels forfollowing and storing the output of said function generator, sequencingmeans for alternately activating said track and hold channels so thatone channel and the other holds during each cardiac period, saidsequencing `means effecting alternate readout of said channels, manuallyvariable means for adding a signal to the output of said channels toapply a patient constant factor to said delay time, Vand meansresponsive to said adding means for converting its output signal to atime base, said converting means being activated by said triggeringsignals so that the pump triggering signals are delayed therefrom.

8. In a heart pump system of the type in which each pumping cycle isinitiated by a signal derived from the patients EKG fwaveform, acomputing circuit for properly delaying triggering of the pumping cyclefrom a predetermined portion of the EKG waveform to compensate forvariations in the duration of the intraventricular waveform with cardiacrate, comprising: means for receiving a signal representing the cardiacperiod, means for receiving a triggering signal representing a selectedportion of the patients EKG waveform, means responsive to said receivingmeans for the ca-rdiac period signal for deriving a signal having anonlinear relationship with said cardiac period signal, and timeconversion means responsive to said derived signal and said triggeringsignal for producing a pump triggering signal delayed from saidtriggering signal in accordance with said nonlinear relationship.

9. The combination as dened in claim 8, wherein said means for derivingsaid nonlinear signal includes a square root circuit, two hold and trackchannels, means responsive to said triggering signal receiving means foralternately connecting said channels to said square root circuit,amplifier means alternately connectable with said track and holdchannels for amplifying the output therefrom, variable emitter followermeans for adding a fixed signal to the output of said amplifying means,said time conversion means including a unijunction circuit responsive tosaid emitter follower, a resettable linear ramp generator for Yfiringsaid unijunction circuit at a time determined by the emitter followermeans, and means responsive to the output of said unijunction circuitand said triggering signal receiving means for resetting said rampgenerator.

References Cited UNITED STATES PATENTS 3,099,260 7/ 1963 Birtwell 128-13,266,487 8/ 1966 Watkins et al 128--1 DALTON L. TRULUCK, PrimaryExaminer.

U.S. Cl. X.R. 128-214 withdrawal servo coil 41 through the same volumeand rate computer circuit.

A pump phase signal, modulated by the volume `and rate computercircuitry in line 42, drives the pump phase driver 43. The magnitude ofthe current in line 42 determines the bias of the pump driver 43 andthereby the magnitude of exitation of the pump servo coil 40. The rateof travel of the pump actuator shaft 50 is directly proportional to themagnitude of the current in the coils 40 and 41.

Pump 60 may be of the reciprocating piston type and is connected todeliver fluid in both directions through catheters 62 and 63. Forarterio-arterial heart assist the catheters 62 and 63 are inserted intothe patients femoral arteries. Then fluid is delivered to the aorta andwithdrawn therefrom in the above described phase relationship with thepatients natural cardiac action.

As shown in FIG. 2, the delay time computer consists generally of afunction generator 66 for deriving an output voltage from the inputvoltage En, (heart cycle period), a manual Vernier 64 for adding apatient constant voltage to the voltage derived by the functiongenerator 66, and a variable delay circuit 65 which converts the outputvoltage from the function generator to a time base relative to thetrigger pulses R from the trigger level selector 13.

As noted above, the desired delay time between the onset of the QRScomplex of the patients EKG waveform and the peak of theintraventricular wave where the pump cycle is to be initiated for properphasing is defined by the equation l0.2l\/R-R+K, where R-R is thecardiac period in milliseconds, and K is a constant number ofmilliseconds for a specific patient.

Referring to FIG. 3 for a more detailed description of the delay timecomputer circuit 15, the equation for the desired delay time TD:l0.21\/R-R+K is solved electronically by converting K and the R to Rperiod to a function of voltage magnitude. Toward this end, a squareroot circuit 70 is `provided consisting of .an operational amplifierwith a diode squaring module as the feedback element. With Em (theapplied voltage from the heart cycle time computer 18 representing thecardiac interval) the square root circuit 70 is constructed to providean output E0=\/10Em.

The function generator 66 consists generally of the square root circuit70, track and hold channel A and channel B, and voltage amplifier 71.The dual channels A and B are necessary to provide a memory capabilityso that during one heart cycle channel A is computing the voltagemagnitude from the square root module 70 and channel B is reading outinto the voltage amplifier 71, and during the next heart cycle channel Awill be read out into the voltage amplifier 71 and channel B willcompute the voltage magnitude from the square root circuit 70. To effectthis timing of the operation of channels A and B a flip-flop FF-l isprovided, which may be a bistable multivibrator, for driving a relaycircuit 73 and hold circuits 74 and 75.

When the flip-flop FF-l is turned on by an R pulse from the triggerlevel selector circuit 13, the voltage in line 77A rises to a higherpotential than line 75, turning transistors 76 and 77 off and transistor78 on Transistor 77 places track or hold module 80 in channel A in itstrack state preparatory to following the output signal from the squareroot circuit 70. Transistor 7 8, now 0n, places track or hold module 82in its hold state so that it stores the signal computed from the squareroot generator circuit 70 on the previous cycle. The track and holdmodules 80 and 82 are of conventional design as will be apparent tothose skilled in this art.

The transistor 76 inthe relay circuit 73 being off deenergizes relay RY1moving contacts 83 to connect channel A with the square root circuit 70and moving contacts 84 to connect channel B with the amplifier 71. Inthis manner, during the heart cycle under consideration, channel Atracks the output voltage from the square root circuit 70 and channel B,which stores the output from the square root circuit on the previouscycle is read out into the operational amplifier 71.

The next succeeding R pulse from the EKG trigger level selector 13changes the state of dip-flop FF-l raising line to a higher potentialthan line 77A, thereby turning on transistors 76 and 77 and turning offtransistor 78. With transistor 77 on, the track or hold module 80changes to its hold state, storing the output from the square rootcircuit 70, and transistor 76 energizes relay RY-l so its contacts 83connect the square root generator 7 0 to channel B and its contacts 84connect channel A to the amplilier 71. During this heart cycle channel Ais read out into the amplifier 71 and channel B tracks the voltageoutput from the square root circuit 70'.

The voltage amplifier 71 amplies the voltage magnitude from the track orhold modules, and produces an output in accordance with the equationEo=l0.21\/Em The manual Vernier circuit 64 consists of an adjustableemitter follower circuit arranged so that the voltage Vk is added to thevoltage from the operational amplifier 71 as desired by the operator.

The conversion of the output voltage from the emitter follower 64 into aperiod of time is accomplished by the variable delay circuit 65 whichincludes a switching circuit 90, a linear ramp generator 91, and aunijunction circuit 92.

A transistor 94 in the linear ramp generator circuit 91 charges acapacitor 95 linearly, which capacitor is connected to the emitter of aunijunction transistor 96. When the ramp voltage across capacitor 95exceeds a certain fraction (1;) of the voltage across the bases B2 andB1, the unijunction transistor fires. Since the base B2 voltage of theunijunction transistor 96 is the voltage which has been computedaccording to the equation l0.2l\/Eml-Vk, the unijunction transistor 96fires when the voltage at the emitter exceeds a value which isproportional to the instantaneous computed voltage on B2.

The transistor switch circuit is provided for synchronizing the rampvoltage in the linear ramp generator with each R pulse. Toward this endthe flip-op FF-Z, which may be a bistable multivibrator, is connected tobe set by an R pulse on line 96, lowering the potential on line 97 toturn off transistor 98. When transistor 98 is turned off, i.e.,nonconductive, capacitor is permitted to charge until the ramp voltageformed thereacross exceeds a fraction 1; of the instantaneous basevoltage across the unijunction transistor 96, at which time an outputpulse occurs at the base B1 of the unijunction transistor 96. This pulseis shaped by a pulse shaper 98 and coupled to a monostable multivibrator100 thereby producing a properly delayed pump cycle triggering pulse tobe applied to the refractory gate 22 for initiation of the push phase ofthe cycle of pump 60.

The output of the monostable multivibrator 100 is also used forresetting the fiip-flop FF-Z (line 102). The appearance of the outputpulse from multivibrator 100 resets the flip-fiop FF-Z, raising thepotential on line 97, and driving the transistor 98 into saturation.This prevents the linear ramp generator from charging capacitor 95 untilthe receipt of another triggering pulse on line 96. When the nexttriggering pulse on line 96 sets flip-flop FF-Z and turns transistorswitch 98 off, capacitor 95 will again begin charging to provide a rampvoltage at the emitter of transistor 96, and another cycle is repeated.

Thus, it is apparent that the variable delay circuit 65 converts a D.C.voltage representing the desired time delay from the emitter follower 64into a pulse delayed from the triggering R pulse by a desired time, byinitiating a ramp voltage with each R pulse at the emitter of aunijunction transistor and by varying the base voltage of theunijunction transistor with the voltage representing the desired delaytime, so that the latter voltage is converted into a

